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AGU Meeting: City stores

It’s not just tropical rainforests that store carbon - cities do too, in features such as soil, vegetation, people, landfill and wood in buildings, furniture and books. In fact, human settlements store 18 Pg of carbon, equivalent to the amount locked up in US croplands. So says Galina Churkina of the Leibniz Centre for Agricultural Landscape Research in Germany, who reckons that the cities of the future could use massive amounts of interior wood panelling to act as a carbon store.

The density of an urban centre also affects its carbon storage potential. Closely-packed areas such as downtown San Francisco are efficient as they release fewer carbon emissions per head and store more carbon per unit area in their tall buildings. But suburban areas store more carbon overall, in lawns and vegetation, although they’re likely to have higher emissions from transport for commuting and shopping.

In a similar vein, Amy Townsend-Small of the University of California, Irvine has been measuring the greenhouse gas emissions from four parks in Orange County, California. If the grass photosynthesizes during the day faster than it respires overnight, on balance it will remove carbon from the atmosphere. And you can increase the chances of this by adding water and fertilizer. But there is a downside - too much fertilization and overwatering can induce the plant to give off nitrous oxide, a greenhouse gas 300 times more powerful than carbon dioxide.

Of the four parks Townsend-Small and co-workers examined, the older sites had stored the most carbon because of carbon accumulation. But the oldest park was a net source of greenhouse gases because of its nitrous oxide release. The newer parks, in contrast, were net greenhouse gas sinks, although the calculations didn’t include carbon emissions from fuel used in park maintenance and from transporting water. Townsend-Small says the research could lead to recommendations for park-managers to use less fertilizer.

Posted by Liz Kalaugher on December 18, 2008 7:41 PM | Permalink